This work is directed towards elucidation of the contribution of histone phosphorylation to the structure and functional regulation of chromatin. The current phase of the work is concentrated on the study of H1 histone phosphorylation and histone phosphorylating enzymes which occur specifically in growing cells. Using methodology capable of examining the phosphorylation of specific sites in H1 histone, we are examining the distribution of phosphate on individual subcomponents of H1 phosphorylated under different conditions of cell growth and cell-cycle blockade, in hopes of determining functional roles for this type of phosphorylation. We are also examining the interaction of highly phosphorylated subcomponents of calf and rat H1 with reconstituted oligonucleosomes in order to determine whether highly phosphorylated H1 molecules have unique properties compatible with a role in chromosome condensation or other functions. Mechanisms for the activation and inactivation of growth-associated histone kinase which occurs as cells enter and leave mitosis are being investigated in purified and partially purified preparations.